The general type and operating principles of PSA, or pressure swing adsorption, apparatus with which this invention is concerned are described in U.S. Pat. Nos. 3,564,816; 3,636,679; 3,717,974; 4,802,899; 5,531,807 and 5,871,564, among others. For example, a pressure swing adsorption apparatus may include two or more adsorbers, each having a fixed sieve bed of adsorbent material to fractionate at least one constituent gas from a gaseous mixture by adsorption into the bed, when the gaseous mixture from a feed stream is sequentially directed through the adsorbers in a co-current direction. While one adsorber performs adsorption, another adsorber is simultaneously purged of its adsorbed constituent gas by part of the product gas that is withdrawn from the first or producing adsorber and directed through the other adsorber in a counter-current direction. Once the other adsorber is purged, the feed stream at a preset time is then directed to the other adsorber in the co-current direction, so that the other adsorber performs adsorption. The first adsorber then is purged either simultaneously, or in another timed sequence if there are more than two adsorbers, all of which will be understood from a reading of the above described patents.
When, for example, such apparatus is used to produce a high concentration of oxygen from ambient air for use in various applications, whether medical, industrial or commercial, air which enters the apparatus typically contains about 78% nitrogen, 21% oxygen, 0.9% argon, and a variable amount of water vapor. Principally, most of the nitrogen is removed by the apparatus to produce a gas product, which for medical purposes, for example, typically may contain at least about 80% oxygen.
The present invention provides a new and improved pressure swing adsorption (xe2x80x9cPSAxe2x80x9d or xe2x80x9coxygen concentratorxe2x80x9d) apparatus, and especially the method of operating the apparatus, that can attain the required concentrations of oxygen for the desired application(s), yet be more productive, more energy efficient and quieter in operation than known multiple bed systems. This is accomplished at least in part by our inventive multiple bed PSA apparatus not exceeding three beds, and an operating cycle that includes operational steps in which beds are purged principally by gases from a then non-producing or xe2x80x9cinactivexe2x80x9d bed, rather than the useful product gas generated by the then producing xe2x80x9cactivexe2x80x9d bed.